The present invention relates to a clutch friction disc for a dry friction clutch, more particularly for a motor vehicle, and also to a friction crown of friction material for equipping such a friction disc.
A motor vehicle dry friction clutch includes, in general terms, a friction disc having two friction crowns, each of which is secured to a support which may be a common support, the support or supports being connected to a splined hub in engagement with a gearbox input shaft. A torsion damping device is, in general, interposed between the support or supports for the crowns and the splined hub. A progressive engagement device is generally disposed between the two crowns, being constituted by the support or supports which have particular arrangements for this purpose, or by an additional device.
The friction disc is, in use, placed between, on the one hand, a reaction plate which is connected directly or indirectly to the crankshaft of the engine of the vehicle, and on the other hand, a pressure plate of a clutch mechanism which includes a cover plate coupled to the reaction plate and an elastic system, which in practice is a spring or so-called diaphragm applying an axial biasing force to the pressure plate, which is coupled in rotation to the cover plate while being able to be displaced axially with respect to the latter by a limited amount.
In the clutch engaged position, the friction crowns of the friction disc are gripped under the effect of the elastic system between the reaction plate and the pressure plate, in such a way that the rotation torque from the heat engine is transmitted to the gearbox input shaft.
Declutching means, which in practice consist of fingers with which the diaphragm is provided, eliminate the effect of the elastic system when a force is applied to them, which, under the effect of return means of the pressure plate acting between the pressure plate and the cover plate, causes the pressure plate to be displaced away from the reaction plate, and therefore causes the friction crowns of the friction disc to be released from being gripped, so that the friction disc, which is mounted for axial movement on the gearbox input shaft, is displaced between the reaction plate and the pressure plate, and the effect of this is to interrupt the transmission of the torque from the engine.
In order that the interruption of the transmission of the torque shall be otal, the declutching operation must be complete, that is to say the friction crowns must no longer be in contact with the reaction plate and the pressure plate.